U.S. patent number 7,396,519 [Application Number 10/764,681] was granted by the patent office on 2008-07-08 for preparation of a high purity and high concentration hydroxylamine free base.
This patent grant is currently assigned to San Fu Chemical Company, Ltd.. Invention is credited to Jin-Fu Chen, Ruey-Shing Chen, Kung-Chin Kuo, Kaung-Far Lin, Wei Te Lin.
United States Patent |
7,396,519 |
Lin , et al. |
July 8, 2008 |
Preparation of a high purity and high concentration hydroxylamine
free base
Abstract
A high purity aqueous solution of hydroxylamine product is
prepared by treating an aqueous solution of hydroxylammonium salt
with a base like ammonia at low temperatures. A novel process can
be carried out by separating the ammonium salt side product from
hydroxylamine with a low temperature filtration and a
resin-exchange process. The concentration of the hydroxylamine
product is further improved by a safe distillation process that
produces a high purity and high concentration hydroxylamine product
with reduced risks of explosion.
Inventors: |
Lin; Kaung-Far (Tainan,
TW), Chen; Jin-Fu (Lucao Township, Chiayi County,
TW), Lin; Wei Te (Youngkang, TW), Chen;
Ruey-Shing (Tainan, TW), Kuo; Kung-Chin
(Youngkang, TW) |
Assignee: |
San Fu Chemical Company, Ltd.
(Taipei, TW)
|
Family
ID: |
34795320 |
Appl.
No.: |
10/764,681 |
Filed: |
January 26, 2004 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20050163694 A1 |
Jul 28, 2005 |
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Current U.S.
Class: |
423/387; 203/6;
203/12 |
Current CPC
Class: |
C01B
21/1463 (20130101); C01B 21/149 (20130101); C01B
21/1445 (20130101) |
Current International
Class: |
C01B
21/00 (20060101) |
Field of
Search: |
;423/387 ;203/6,12 |
References Cited
[Referenced By]
U.S. Patent Documents
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4778669 |
October 1988 |
Fuchs et al. |
4956168 |
September 1990 |
Wagaman |
5472679 |
December 1995 |
Levinthal et al. |
6299734 |
October 2001 |
Watzenberger et al. |
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Foreign Patent Documents
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3528463 |
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Feb 1987 |
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DE |
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WO-97/22551 |
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Jun 1997 |
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WO |
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Primary Examiner: O'Sullivan; Peter
Attorney, Agent or Firm: The SUN Law Office Sun;
Hsiang-ning
Claims
What we claim is:
1. A process for preparing a high purity and high concentration
hydroxylamine product, the process comprises a. feeding an aqueous
feed solution containing a hydroxylammonium salt at a maximum
concentration and a stabilizer into a reactor at a low temperature;
b. neutralizing the aqueous feed solution with a base to form a
slurry until the pH of the resulting slurry reaches in a range of
from about 9.0 to about 12.0; c. adding an additional amount of
solid of the hydroxylammonium salt to increase the total amount of
the hydroxylammonium salt in the reactor before or during
neutralization of step b; d. separating the resulting slurry into
an aqueous solution phase and a solid phase at a temperature
between about -20.degree. C. to about 20.degree. C.; e. treating
the aqueous solution phase in at least one ion exchange column
containing at least one ion exchange resin to produce a high purity
hydroxylamine solution thereby the resistivity is not lower than
about 10 Megohms-cm; and f. concentrating the high purity
hydroxylamine solution at a sub-atmospheric pressure to form the
high purity and high concentration hydroxylamine product.
2. The process of claim 1, wherein the hydroxylammonium salt is a
salt of a mineral acid selected from the group consisting of
hydroxylammonium sulfate, hydroxylammonium nitrate,
hydroxylammonium chloride and mixtures thereof.
3. The process of claim 2, wherein the hydroxylammonium salt
consists essentially of hydroxylammonium sulfate.
4. The process of claim 1, wherein the base is selected from a
strong base or a weak base, wherein the strong base is selected
from sodium hydroxide, potassium hydroxide and mixtures thereof;
and the weak base is selected from ammonia, ammonium hydroxide,
volatile alkylamines, cyclic amines and mixtures thereof.
5. The process of claim 4, wherein the base is ammonia.
6. The process of claim 1, wherein the stabilizer is a compound
selected from the group consisting of hydroxyanthraquinone,
substituted hydroxyanthraquinones, thiourea, substituted thioureas,
hydroxyurea, substituted hydroxyureas, aminoquinoline, substituted
aminoquinolines, phenanthroline, substituted phenanthrolines, one
or more polyhydroxyphenols, cyclohexanediaminetetraacetic acid,
thiamine or its derivatives, ethylenediaminetetraacetic acid or its
derivatives, and mixtures thereof.
7. The process of claim 6, wherein the stabilizer consists
essentially of cyclohexanediaminetetraacetic acid.
8. The process of claim 1, wherein the neutralization is conducted
at a temperature in the range of from about 5.degree. C. to about
65.degree. C.
9. The process of claim 1, wherein the neutralization is conducted
at a temperature in the range of from about 10.degree. C. to about
55.degree. C.
10. The process of claim 1, wherein the neutralization is conducted
at a temperature in the range of from about 15.degree. C. to about
45.degree. C.
11. The process of claim 1, wherein the hydroxylammonium salt
consists essentially of hydroxylammonium sulfate and the ratio of
the additional amount of the solid added to the amount of
hydroxylammonium sulfate in the aqueous feeding solution is in the
range of from about 0 to about 4.8 on a weight to weight basis.
12. The process of claim 11, wherein the ratio is in the range of
from about 0.5 to about 4.6.
13. The process of claim 11, wherein the ratio is in the range of
from about 0.6 to about 4.5.
14. The process of claim 1, wherein separation in step d is
conducted by centrifugation, filtration, or combination
thereof.
15. The process of claim 14, wherein the temperature of step d is
between about -10.degree. C. to about 15.degree. C.
16. The process of claim 14, wherein the temperature of step d is
between about 5.degree. C. to about 15.degree. C.
17. The process of claim 1, wherein the base is ammonia, the
hydroxylammonium salt consists essentially of hydroxylammonium
sulfate, and the aqueous solution phase contains greater than 50%
of hydroxylamine after removal of ammonium sulfate and residual
ammonia.
18. The process of claim 1, wherein the ion-exchange resin is
selected from the group consisting of cation-exchange resin,
anion-exchange resin, and mixtures thereof thereby ammonium cation
and anions of mineral acids are removed.
19. The process of claim 18, wherein the anion exchange resin is
selected from one or more strong base gel resins, one or more
macroporous resins, or mixtures thereof.
20. The process of claim 18, wherein the cation exchange resin is
selected from one or more strong acid gel resins, one or more
macroporous resins, or mixtures thereof.
21. The process of claim 18, wherein the ion exchange process is
carried out in four stages: A. feeding the aqueous solution phase
into a first column containing the anion exchange resin until
breakthrough of salt anions in the effluent; B. regenerating the
anion exchange resin with sulfuric acid to form a sulfate form
followed by converting the sulfate form into an hydroxide form; C.
feeding the effluent from stage A into a second column containing
the cation exchange resin until breakthrough of ammonium ion; and
D. regenerating the cation exchange resin with sulfuric acid.
22. The process of claim 1, wherein the process is carried out in a
continuous moving bed or simulated moving bed ion exchange
apparatus.
23. The process of claim 1, wherein the concentration step f is
conducted under the sub-atmospheric pressure in the range of from
about 6 torrs to about 100 torrs [about 0.8 kPa to about 13.3
kPa].
24. The process of claim 1, wherein the sub-atmospheric pressure in
the range of from about 10 torrs to about 80 torrs [about 1.33 kPa
to about 10.7 kPa].
25. The process of claim 1, wherein the sub-atmospheric pressure in
the range of from about 10 torrs to about 60 torrs [about 1.33 kPa
to about 8.0 kPa].
26. The process of claim 1, wherein the temperature for the
concentration step f is in the range of from about 25.degree. C. to
about 60.degree. C.
27. The process of claim 1, wherein the temperature for the
concentration step f is in the range of from about 30.degree. C. to
about 50.degree. C.
28. The process of claim 1, wherein the temperature for the
concentration step f is in the range of from about 35.degree. C. to
about 45.degree. C.
29. The process of claim 1, wherein temperature change during
neutralization step b is maintained within a range of from about 0
to about 25.degree. C.
30. A process for preparing a high purity and high concentration
hydroxylamine product, the process comprises: a. feeding an aqueous
feed solution containing a hydroxylammonium salt consisting
essentially of hydroxylammonium sulfate at a maximum concentration
and a stabilizer consisting essentially of
cyclohexanediaminetetraacetic acid into a reactor at a low
temperature; b. neutralizing the aqueous feed solution at a
temperature in the range of from about 15.degree. C. to 45.degree.
C. with a base to form a slurry until the pH of the resulting
slurry reaches in a range of from about 9.0 to about 12.0; c.
adding an additional amount of solid of hydroxylammonium sulfate
wherein the ratio of the additional amount of solid added to the
amount of hydroxylammonium sulfate in the aqueous feeding solution
is in the range of from 0.6 to 4.5 on a weight to weight basis to
increase the total amount of hydroxylammonium sulfate in the
reactor before or during neutralization of step b; d. separating
the resulting slurry by centrifugation and filtration into an
aqueous solution phase and a solid phase at a temperature between
about 5.degree. C. to about 15.degree. C.; e. treating the aqueous
solution phase in a first column containing anion exchange resin to
form an effluent followed by treating the effluent from the first
column in a second column containing a cation exchange resin to
produce a high purity hydroxylamine solution thereby the
resistivity is in the range of from about 10 Megohms-cm to about 50
Megohms-cm; and f. concentrating the high purity hydroxylamine
solution at a sub-atmospheric pressure in the range of from about
10 torrs to about 60 torrs [about 1.33 kPa to about 8.0 kPa] and a
temperature in the range of from about 35.degree. C. to about
45.degree. C. to form the high purity and high concentration
hydroxylamine product.
31. The process of claim 30, wherein the aqueous solution phase
contains greater than 50% of hydroxylamine after removal of
ammonium sulfate and residual ammonia.
Description
BACKGROUND OF THE INVENTION
The present invention relates to a process for the manufacture of a
high purity and high concentration aqueous solutions of
hydroxylamine. Hydroxylamine free base (hereinafter H.sub.2NOH, HA
or HAFB) is a specialty chemical widely used in the pharmaceutical,
agricultural chemical and electronic industries. Potential
applications of HA-related chemicals are also possible in
automotive, aerospace industries and as an oxidant for various
formulations in liquid propellants.
Since its introduction by Nissin Chemical Co., Ltd. of Japan in the
early 1970, the commercial product has been shipped as a 50%
aqueous solution for more than 30 years now. The rapid growth of
the use of HA in the semiconductor industry accounts for the
increase of the market demand in the recent years. A double-digit
growth in 2003 has been projected by a marketing study. In
addition, a successful commercialization of the HA-related liquid
propellants for air bags and a monopropellant thruster will, for
sure, increases the demand in the market further.
There are three basic manufacturing technologies that have been
disclosed in the patent literature: Reaction of a base with a
hydroxylamine salt (neutralization process); Ion-exchange process;
Electrochemical process.
In the neutralization process, once the free base is liberated, the
process involves additional steps to achieve a 50% concentration
product and with extremely high purity. These additional process
steps include: Separation and removal of side products;
Concentration of the hydroxylamine to a desired concentration
level; and Purification of the product to a purity required for the
intended applications.
Depending on the applications in different industries, the desired
and sometimes required metal impurity levels, especially those of
transition metals such as iron, cobalt, chromium, can vary from
hundreds of ppm to several ppb. Furthermore, the stability of a
hydroxylamine product depends on temperature, hydroxylamine
concentration, metal impurity levels and other factors. Therefore,
the concentration and purification process chosen for producing the
desired product specification is extremely critical.
Many attempts have been disclosed by various inventors for the
preparation of hydroxylamine using hydroxylamine salts with various
bases.
For example, DE-A-3528463 discloses the neutralization with
calcium, strontium, or barium hydroxide. The removal of finely
divided alkaline earth metal sulfate side products presents
considerable difficulties. In addition, calcium sulfate side
product has a relatively high solubility, thus it cannot be totally
removed by filtration. Strontium hydroxide and barium hydroxide are
highly priced and known to be quite toxic.
U.S. Pat. No. 5,472,679 describes a process for the preparation of
hydroxylamine by reacting a hydroxylamine sulfate (HAS) solution
with a suitable base at up to 60.degree. C. The resulting mixture
is distilled to dryness under reduced pressure at <65.degree. C.
During the distillation, the metal impurity concentration increases
along with the HA concentration, thus risking the danger of
explosion.
U.S. Pat. No. 4,956,168, DE-A-1247282, and EP-A-108294 disclose a
process in which alcoholic solutions of free hydroxylamine are
obtained by reacting hydroxylammonium sulfate with ammonia in an
alcohol solvent followed by removing the precipitated ammonium
sulfate side product. However, owing to the flammability of the
alcohol solutions and the high expense in recovery of the alcohol
solvents, this process is difficult to be commercialized at a large
scale.
DE-A-3601803 describes the use of lower alcohol solvents. The
precipitated ammonium sulfate side product is separated, water is
added and the alcohol is distilled off from the solution. Again,
the flammability of the lower alcohol solvents and the instability
of the hydroxylamine prohibit the industrial application of the
process.
WO97/22551 discloses a process by which a solution, resulting from
neutralization of HAS with a suitable base, is separated into an
aqueous hydroxylamine fraction and a salt solution by distillation
at a temperature above 80.degree. C. (stripping). The HA fraction
is further concentrated in a distillation column. With a strong
base such as sodium hydroxide, a complete neutralization is
obtained. However, the ready decomposition of HA, its sensitizing
effect, and the tendency of sodium sulfate to cake make the process
difficult to practice industrially.
The use of aqueous ammonium hydroxide as a base would have two
major advantages over sodium hydroxide: i) lower cost, and ii) no
metal contamination. However, ammonium hydroxide is a relatively
weak base, only 60-70% conversion is observed under the above
stripping procedure. Therefore, the use of ammonium hydroxide is
not viable with the stripping method of WO 97/22551.
U.S. Pat. No. 6,299,734 B1 discloses a process by which the
hydroxylammonium salt in an aqueous phase is treated with ammonia
by a countercurrent method and at the same time the solution
obtained is separated into an aqueous hydroxylamine solution and a
salt fraction by stripping with steam in a stripping/reaction
column. In a particularly preferred embodiment, the neutralization
of hydroxylamine salt with ammonia is carried out by the
countercurrent method and the stripping of the hydroxylamine from
the salt solution is effected in combination with partial
concentration of the hydroxylamine solution in only one column,
i.e. a stripping/reaction/distillation column. The process improves
over the simple stripping process by increasing the yield of
hydroxylamine from about 60% to 90%. However, the
stripping/reaction/distillation process employs substantial amount
of steam. Not only the energy cost on the steam used is high,
additional energy is also required to concentrate the hydroxylamine
product because of low hydroxylamine concentrations produced from
the process to avoid the hydroxylamine decomposition when exposed
to >80.degree. C. temperature during the manufacturing
process.
SUMMARY OF THE INVENTION
The instant invention is related to a process for preparing a high
purity and high concentration hydroxylamine free base product. The
process comprises a.) feeding an aqueous feed solution containing a
hydroxylammonium salt at a maximum concentration and a small amount
of a stabilizer into a reactor at a low temperature; b.)
neutralizing the aqueous feed solution with a base to form a slurry
until the pH of the resulting slurry reaches 9.0 to 12.0; c.)
adding an additional amount of a solid of the hydroxylammonium salt
to increase the total amount of the hydroxylammonium salt in the
reactor before or during neutralization; d.) separating the
resulting slurry into an aqueous solution phase and a solid phase
at a temperature between -20 to 20.degree. C.; e.) treating the
aqueous solution phase in at least one an ion exchange column
containing at least one ion exchange resin to produce a high purity
hydroxylamine solution thereby the resistivity is not lower than
about 10 Megohms-cm; and f.) concentrating the high purity
hydroxylamine solution at a sub-atmospheric pressure to form the
high purity and high concentration hydroxylamine product.
It is another aspect of the instant invention relates to a process
for preparing a high purity and high concentration hydroxylamine
product, the process comprises: a.) feeding an aqueous feed
solution containing a hydroxylammonium salt consisting essentially
of hydroxylammonium sulfate (also referred to as hydroxylamine
sulfate) at a maximum concentration and a stabilizer consisting
essentially of cyclohexanediaminetetraacetic acid into a reactor at
a low temperature; b.) neutralizing the aqueous feed solution at a
temperature in the range of from about 15 to 45.degree. C. with
ammonia gas to form a slurry until the pH of the resulting slurry
reaches 9.0 to 12.0; c.) adding an additional amount of solid of
hydroxylammonium sulfate wherein the ratio of the additional amount
of solid added to the amount of hydroxylammonium sulfate in the
aqueous feeding solution is in the range of from 0.6 to 4.5 on a
weight to weight basis to increase the total amount of
hydroxylammonium sulfate in the reactor before or during
neutralization; d.) separating the resulting slurry by
centrifugation and filtration into an aqueous solution phase and a
solid phase at a temperature between about 5 to about 15.degree.
C.; e.) treating the aqueous solution phase in a first column
containing anion exchange resin to form an effluent followed by
treating the effluent in a second column containing a cation
exchange resin to produce a high purity hydroxylamine solution
thereby the resistivity is in the range of from about 10 Megohms-cm
to about 50 Megohms-cm; and f.) concentrating the high purity
hydroxylamine solution at a sub-atmospheric pressure in the range
of from about 10 torrs to about 60 torrs [about 1.33 kPa to about
8.0 kPa] and a temperature in the range of from about 30.degree. C.
to about 40.degree. C. to form the high purity and high
concentration hydroxylamine product.
It is a further object that the ion exchange step is carried out in
two to four stages: A. feeding the aqueous solution phase into a
first column containing the anion exchange resin until breakthrough
of salt anions in the effluent; B. (optional) regenerating the
anion exchange resin with sulfuric acid to form a sulfate form
followed by converting the sulfate form into an hydroxide form; C.
feeding the effluent from stage A into a second column containing
the cation exchange resin until breakthrough of ammonium ion; and
D. (optional) regenerating the cation exchange resin with sulfuric
acid.
It is yet another aspect of the present invention that the process
is carried out in a fixed bed, continuous moving bed, or simulated
moving bed ion exchange apparatus.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows temperature profiles of four separate tests in Example
5 during which an aqueous solution hydroxylammonium salt is
neutralized with a base. The reactor temperature is recorded as a
function of time.
FIG. 2 shows the changes of pH values during the same tests.
FIG. 3 shows temperature profiles of four separate tests in Example
6 during which an aqueous solution hydroxylammonium salt is
neutralized with a base. The reactor temperature is recorded as a
function of time.
FIG. 4 shows the changes of pH values during the same tests.
DESCRIPTION OF THE INVENTION
It is one object of the present invention to provide a new,
innovative, economical and safe process for the production of a
high purity and high concentration hydroxylamine free base which
can be carried out utilizing strong bases such as sodium hydroxide,
potassium hydroxide, or weak bases such as ammonia, preferably in
the gaseous form, volatile alkylamines, cyclic amines and mixtures
thereof, for the complete liberation of hydroxylamine from its
salt.
We have unexpectedly discovered that the object can be achieved by
neutralizing hydroxylammonium salt with ammonia gas at a low
temperature to obtain high yields with high hydroxylamine
concentrations. The ammonium salt side product (also referred to as
byproduct) can be separated from the free base again at low
temperatures by a combination of filtration and ion-exchange, thus
avoiding the reversible reaction that typically occurs quickly at
high temperatures. Being of high purity and relatively high
concentration after these steps, the hydroxylamine can be further
distilled under vacuum at a relatively low temperature to obtain a
desired high concentration at the bottom with minimum decomposition
and reduced risks of explosions.
This invention relates to a process for an economic production of
high purity and high concentration hydroxylamine by neutralizing a
hydroxylammonium salt with ammonia gas to its completion and
removing the reaction side product at low temperatures to prevent
the reversible reaction thus achieving high product yield. In
addition, due to the high purity nature of the product generated by
the present process, any subsequent concentration step can be
performed rather safely.
The present process comprises several steps: neutralization of
hydroxylammonium salt with a base, preferably a weak base such as
ammonia; separation of the ammonium salt side product at low
temperatures; and concentration of the highly pure
hydroxylamine.
Neutralization
It is well known that the treatment of a hydroxylammonium salt with
a base will liberate hydroxylamine free base. The hydroxylammonium
salts used are generally the salts of mineral acids in the aqueous
solution. These acids include sulfuric acid, hydrochloric acid,
nitric acid and phosphoric acid. A preferred hydroxylammonium salt
is or consists essentially of hydroxylammonium sulfate.
Both strong bases and weak bases can be used for the present
invention. Strong bases include, but are not limited to, sodium
hydroxide, potassium hydroxide, rubidium hydroxide, cesium
hydroxide, and mixtures thereof. Weak bases include, but are not
limited to, ammonium hydroxide, ammonia (liquid and gas forms, or
mixtures), volatile bases such as alkylamines (C1-C6 amines such as
methylamine, ethylamine, dimethylamine, etc.), and cyclic amines
such as cyclohexylamine and their mixtures. Ammonia gas is a
preferred weak base for ease of operation and other chemical and
physical properties. Liquid ammonia also may be used under certain
conditions to control the exothermicity of the neutralization
reaction in the neutralization reactor.
By using strong bases such as sodium hydroxide or potassium
hydroxide, hydroxylamine can be completely liberated from its
hydroxylammonium salt. A weaker base such as ammonium hydroxide and
other volatile bases including alkylamines and cyclic amines could
not displace hydroxylamine completely due to the neutralization
equilibrium: (H.sub.3NOH).sub.2X+2 ROH=R.sub.2X+2 H.sub.2NOH+2
H.sub.2O (1)
In this equation, X is an example of a dibasic acid anion such as
sulfate, SO.sub.4.sup.=, derived from sulfuric acid; and R is
NH.sub.4.sup.+.
For using ammonium hydroxide as the base and hydroxylamine sulfate
as the neutralization feed, the solubility of ammonium sulfate in
water at 100.degree. C. is relatively high, 51% by weight. This
solubility decreases as the temperature decreases. This will lower
the driving force from reversing the neutralization to the left of
equation 1.
If ammonia gas is used as the weak base for neutralization and X is
again an example of a dibasic acid anion such as sulfate,
SO.sub.4.sup.=, then the reaction is represented by equation (2) as
shown below: (H.sub.3NOH).sub.2X+2
NH.sub.3+2H.sub.2O=(NH.sub.4).sub.2X +2 H.sub.2NOH+2H.sub.2O
(2)
For the present invention, the neutralization step is conducted at
a temperature in the range of from about -25.degree. C. to about
25.degree. C., preferably from about -20.degree. C. to about 10C.
The heat of neutralization may raise the temperature of the reactor
and its contents to <30.degree. C. before it is lowered to the
initial temperature.
The hydroxylamine sulfate or other similar feed solutions are
typically introduced into the neutralization reactor at a low
temperature, which is in the range of from about -25.degree. C. to
about 25.degree. C., preferably from about -20.degree. C. to about
10.degree. C. This low temperature is often and preferably selected
to be close to or the same as the initial neutralization
temperature.
The concentration of the hydroxylamine produced from the
neutralization reaction depends not only on the yield of the
process but on the amount of water brought to the reactor. In the
present invention, it is preferred that the hydroxylammonium salt
and the base of the highest or maximum possible concentrations
under the reaction condition are used. For example a 25-33% by
weight of hydroxylammonium sulfate solution in water is used
initially, representing the saturation concentrations of HAS in
water at a particular neutralization temperature and other reaction
conditions. Also preferably, ammonia gas instead of ammonium
hydroxide solution is introduced into the neutralization
reactor.
Before or while the neutralization is in progress, it is
advantageous that an additional amount of hydroxylamine sulfate, or
any other hydroxylammonium salt selected as the starting material
for the process, preferably in the form of solids or crystals or
powders, are added to increase the HA product concentration. The
ratio of this additional amount of the solid added to the amount of
hydroxylammonium sulfate in the aqueous feeding solution is in the
range of from about 0 to about 4.8, preferably from about 0.5 to
about 4.6, and more preferably from about 0.6 to about 4.5, all on
a weight to weight basis.
It is also preferred that an excess amount of the weak base is
added to drive the equilibrium to the right of Equation 1. As an
example, using hydroxylammonium sulfate and ammonia, an excess
amount of ammonia at 10 to 30% by weight in the final product
solution over the total amount of ammonia needed to neutralize
hydroxylammonium sulfate--including any additional amount of
hydroxylammonium sulfate solid or crystal added--in the product
solution is used to ensure a complete neutralization at a
temperature in the range of from about 0C. to about 10.degree.
C.
Alternatively, another preferred method for the neutralization is
the addition of hydroxylammonium salt crystal to the water solution
of a base. In the case of ammonium hydroxide and hydroxylammonium
sulfate, the aqueous solution of ammonium hydroxide with an ammonia
content of ranging from 18 to 29 weight percents is first added to
the reactor and then hydroxylammonium sulfate in the form of
crystal or powder is then added in one total sum or in separate
sequential amount to match the amount of ammonium hydroxide in the
basic solution. As the neutralization progresses, the pH of the
solution will decrease. As the neutralization is completed,
typically at a pH of between about 8 and about 9, ammonia is added
to the product solution until the pH is at between about 12 and
about 12.5.
Stabilizer(s), typically chelating agents that are capable of
binding metal ions in the pH range of the aqueous hydroxylamine
solution and by themselves are anions, are preferably added before
the neutralization step. A preferred mode is to have at least one
stabilizer in the aqueous feed solution containing the
hydroxylammonium salt.
Examples of suitable stabilizers include, but are not limited to
hydroxyanthraquinone, substituted hydroxyanthraquinones, thiourea,
substituted thioureas, hydroxyurea, substituted hydroxyureas,
aminoquinoline, substituted aminoquinolines, phenanthroline,
substituted phenanthrolines, one or more polyhydroxyphenols,
cyclohexanediaminetetraacetic acid, thiamine or its derivatives,
ethylenediaminetetraacetic acid or its derivatives, other
chemically similar compounds, and mixtures thereof. A preferred
stabilizer is cyclohexanediaminetetraacetic acid.
The concentration of the stabilizer is typically from about 20 to
about 50,000 ppm by weight. Preferably, it is from about 50 to
about 5,000 ppm by weight. Most preferably, it is from about 100 to
about 500 ppm by weight.
The neutralization step can be carried out in a number of known
reactor systems or configurations. For example, the reactor can be
a conventional vessel, counter-current reactor, co-current reactor
or any other types known to those skilled in the art. If ammonia
gas is used as the weak base, it can be distributed into the
reactor via any known gas distribution methods such as sparging.
Additional mixing can be achieved by using many known methods such
as agitation with moving/rotating baffles, stirring, blending, or
through fixed parts designed into the reactor itself. Because the
neutralization reaction is exothermic, it is preferred to
incorporate such additional mixing mechanism into the reactor
system to have better and more even temperature distribution and
control. The temperature change in this step is generally
controlled within a range of from about 0 to about 35.degree. C.,
preferably from about 0 to about 25.degree. C., more preferably
from about 5 to about 20.degree. C. If a base such as ammonia is
introduced into the system at a temperature lower than the
temperature of the solution containing the hydroxylammonium salt,
there could be a temperature drop initially.
The side product, ammonium salt such as ammonium sulfate, typically
has limited solubility in the neutralization product mixture,
particularly at low temperatures. As a result, the neutralization
step typically produces a slurry product with a solid phase and an
aqueous solution (liquid) phase. It is preferred that at the end of
the neutralization step the pH of the slurry is in the range of
from at least 7.0 to about 14, preferably from about 8 to 13, and
more preferably from about 9 to about 13. It is preferred that
hydroxylammonium sulfate is used as the hydroxylammonium salt and
an HA solution of greater than (>) 50% by weight can be prepared
in one neutralization step after the removal of the excess ammonia
(used as the base) and the ammonium sulfate dissolved in the
solution (see Example 6).
Filtration
The precipitated ammonium salt (solid phase) in the slurry is
removed by centrifugation and/or filtration (such as vacuum
filtration) at such low temperatures. Any conventional or known
centrifugation and/or filtration methods can be used. Depending the
solid content in the product slurry, solid particle size, pH and
other factors, sometimes it is preferred to use both centrifugation
and filtration to achieve maximum solid salt removal.
A preferred low temperature range for carrying out the filtration
is in the range of from about -20.degree. C. to about 10.degree. C.
A more preferred temperature range is from about -5.degree. C. to
about 5.degree. C. Under this solid-liquid separation, majority of
the ammonium sulfate precipitate is removed. A solution containing
at least 50% (by weight) of HA scan be preferably produced and/or
recovered after the neutralization step is carried out and after
the removal of the excess base (such as ammonia) and the dissolved
side product salt such as ammonium sulfate. (see Example 6)
However, even at these low temperatures, an ammonium salt like
ammonium sulfate still maintains certain solubility in the liquid
aqueous solution phase of the hydroxylamine product slurry. For the
present invention, it is preferred that this residual salt still
dissolved in the aqueous solution phase is removed by ion-exchange
in a reactor or column containing at least one anion-exchange resin
to achieve the desired high purity of the hydroxylamine
product.
Ion-exchange
The second step of the separation of ammonium sulfate from the
aqueous solution of hydroxylamine is by an ion-exchange process. An
anion-exchange resin in the OH-form is used to remove sulfate ion
or other anions from the aqueous solution. Suitable resins include,
but are not limited to, macroporous anion exchange resins, strong
basic gel resins, and mixtures thereof. Many commercial anion
exchange resins that are capable of exchanging sulfate (or nitrate,
chloride, phosphate etc) with OH.sup.- ion are adequate for the
removal of sulfate ion and other similar anions. As examples, Rohm
and Haas Amberjet.RTM. 4400, Sybron lonac.RTM. ASB-1, and
Mitsubishi SAT 10L and SAT 20L are particularly effective exchange
resins for the removal of sulfate ions. All the trademarks of such
commercially available ion exchange resins belong to their
respective owners.
This anion ion-exchange step of the present invention can be
carried out in a fixed bed, continuous moving bed or simulated
moving bed ion exchange apparatus/reactor. The treatment is
continued until the anion appears in the outlet of the exchange
bed. At this point, the anion ion exchange resin can be regenerated
by treatment with a strong mineral acid such as sulfuric acid to
form a suitable form such as a sulfate form. Following this, the
anion resin is converted to the OH form by methods known to those
skilled in the art. This regeneration can be carried out either "on
line" as part of the entire process, or "off line" in an isolated
reaction vessel. If an array of anion ion exchange resin columns
(reactors) is present, each column can be switched on or off
independently.
During the anion-exchange step, the pH of the aqueous solution is
preferably maintained at equal to or greater than about 7.0 to
enhance the equilibrium to the right side of Equations (1) or (2).
Atypical pH range is from about 7 to about 14. A preferred pH range
is from about 8 to about 11. A more preferred pH range is from
about 8.5 to about 10.
Because the aqueous hydroxylamine solution also contains ammonium
and metal ions, it is desirable to remove these ions, particularly
transition metal ions such as iron, cobalt, and others. One
optional additional step is to treat the aqueous solution with one
or more cation ion exchange resions. This treatment can be
performed before or after the anion exchange resin treatment. It is
preferred that this cation exchange resin treatment is carried out
after the anion exchange resin treatment. Suitable resins include,
but are not limited to, macroporous cation exchange resins, strong
acid gel resins, and mixtures thereof Commercially available cation
exchange resins suitable for this purpose include, but are not
limited to, Rohm and Haas Amberjet.RTM. 1500, IONAC.RTM. CPF-110,
Dowex.RTM. HGR-W2, and Mitsubishi SKT 10L and SKT 20L. A preferred
resin is Mitsubishi SKT 20L. All the trademarks of such
commercially available ion exchange resins belong to their
respective owners.
This cation ion-exchange step of the present invention can be
carried out in a fixed bed, continuous moving bed or simulated
moving bed ion exchange apparatus/reactor. The treatment is
continued until the ammonium cation or metal ion is observed in the
effluent. At this point, the cation ion exchange resin can be
regenerated by treatment with a strong mineral acid such as
sulfuric acid. This regeneration can also be carried out either "on
line" as part of the entire process, or "off line" in an isolated
reaction vessel. If an array of cation ion exchange resin columns
(reactors) is present, each column can be switched on or off
independently.
One preferred criterion to measure the high purity of the
ion-exchanged product is the resistivity of the resultant aqueous
hydroxylamine solution. The higher the resistivity is, the higher
the purity of the HA containing solution. For the present
invention, the resistivity of a high purity hydroxylamine solution
after ion-exchange is not lower than about 75 Megohms-cm,
preferably not lower than about 50 Megohms-cm, more preferably in
the range of from about 10 Megohms-cm to about 50 Megohms-cm. This
resistivity measurement can be carried out by many methods or
instrument known to those skilled in the art.
Concentration
The aqueous solution obtained from the filtration, anion-exchange
and optional cation-exchange steps is essentially free from metal
and anion impurities, i.e. the resistivity is not lower than those
prescribed levels disclosed above. As well known to those skilled
in the art, resistivity is in inverse relationship with
conductivity. Furthermore, the hydroxylamine concentration in the
aqueous solution before the concentrations step is typically in the
range of from about 15 to about 55% by weight, preferably from
about 20 to about 50% by weight, and more preferably from about 30
to about 50% by weight.
Since the aqueous hydroxylamine solution is quite pure and it is
essentially free of metal ions, especially it is substantially free
[less than about 100 ppb] of transition metals, the concentration
process can be performed with a simple distillation with a high
degree of safety. As the distillation progresses the hydroxylamine
concentration in the distillation bottom increases and so is the
metal concentration. Therefore, it is desirable to distill under
reduced (sub-atmospheric) pressure and lower temperature to
minimize hydroxylamine decomposition. The temperature is typically
from about 25.degree. C. to about 60.degree. C., preferably from
about 30.degree. C. to about 50.degree. C., and more preferably
from about 35.degree. C. to about 40.degree. C. A reduced (or
sub-atmospheric) pressure is generally in the range of from about 6
torrs to about 100 torrs [about 0.8 kPa to about 13.3 kPa],
preferably about 10 torrs to about 80 torrs [about 1.33 kPa to
about 10.7 kPa], more preferably about 10 torrs to about 60 torrs
[about 1.33 kPa to about 8.0 kPa].
The distillation can be conducted with any distillation columns or
reactors or configurations that are known commercially or to those
skilled in the art. The vacuum requirement and operational
procedures/parameters are appropriately chosen to optimize the
distillation efficiency and economics. The high concentration
attainable after the concentration step is typically in the range
of from about 35 wt % to about 55 wt %.
The following examples illustrate the principles and advantages of
the present invention. Examples 1-3 are comparative examples
showing the preparation of hydroxylamine free base from the
neutralization of hydroxylamine sulfate with three bases, sodium
hydroxide, potassium hydroxide and ammonia.
EXAMPLE 1(COMPARATIVE)
To a 500-mL three-neck Pyrex.RTM. round-bottom flask, 291.54 grams
of a 45.63% by weight potassium hydroxide were added. The reactor
was cooled with a ice-water bath at 4.degree. C. and the solution
was stirred with a Teflon-coated stirrer. 194.45 grams of
hydroxylamine sulfate (>99.0% purity) were added to the reactor
gradually. Occasionally, the reactor was shaken manually to improve
the mixing. All these operations were conducted in a Class 100
clean room. At the end of the neutralization, the product solution
was centrifuged at 4000 rpm and the clear solution was decanted.
The product was analyzed with an automatic titrator (Kyoto
Electronics, Model AT-500).
Results of the analysis showed a potassium sulfate of 5.41% and a
hydroxylamine concentration of 18.67% by weight.
EXAMPLE 2 (COMPARATIVE)
Following a general procedure of Example 1, 240.28 grams of a 50%
sodium hydroxide solution were introduced into the 500-mL
neutralization reactor. 226.45 grams of hydroxylamine sulfate
(>99.0% purity) were added to the reactor gradually.
Results of the titration analysis on the clear product solution
showed a sodium sulfate of 5.16% and a hydroxylamine concentration
of 18.45% by weight.
EXAMPLE 3 (COMPARATIVE)
Following a general procedure of Example 1, 246 grams (200mL) of a
33.0% hydroxylamine sulfate solution were introduced into the
500-mL reactor which was placed in clean bag. An electronic grade
ammonia was fed into the reactor at a slow flow rate. The
neutralization was terminated at a pH value of 9.0.
The product solution was filtered under vacuum with a Teflon.RTM.
filter of 0.3 micrometer pore opening. The filtrate was analyzed
with the automatic titrator.
Following the general procedure of Example 1, 300 milliliters (mL)
of a 33.0% hydroxylamine sulfate solution were neutralized with
ammonia gas in a 500-mL reactor. This was repeated with 800 mL of
the 33.0% hydroxylamine sulfate solution in a 1000-mL reactor.
Several runs were conducted, results are summarized in Table 1
along with other neutralization runs.
TABLE-US-00001 TABLE 1 Results of analysis on products from Example
3 Vol. of HA before HA after Run HAS pH before filtration PH after
filtration number (mL) filtration (wt %) filtration (wt %) 1 200
9.48 12.15 9.48 13.50 2 200 9.73 12.63 9.83 12.85 3 300 9.17 12.17
8.89 12.25 4 300 9.25 12.47 9.25 13.14 5 800 9.50 11.73 9.25 12.09
6 800 9.22 11.28 9.36 12.56 7 800 9.09 11.87 8.85 12.50 8 800 9.17
11.64 9.20 12.08
EXAMPLE 4 (INVENTION)
Following a general procedure of Example 3, 200 milliliters (mL) of
33% HAS were neutralized with ammonia in a 500-mL reactor. Before
the start of or during the addition of the base, about 150 grams of
HAS crystal were also added to the reactor. After about 90 minutes,
the reactor temperature was lowered to about 10.degree. C. and the
neutralization was completed. The reaction product was separated
into two portions by a vacuum filtration: a filtrate and a filter
cake.
The filter cake was dried in an oven at 105.degree. C. for a period
of more than 15 hours. The dried filter cake was dissolved in water
and the contents of ammonium sulfate (AmS) and hydroxylammonium
sulfate (HAS) were determined by titration. Reaction yields were
calculated using analytical results obtained for HA, AmS and HAS as
shown in Tables 2 and 3. Results of this example show that
unexpectly a yield of much greater than 90% can be achieved by
neutralizing hydroxylamine sulfate with a weak base such as ammonia
and the solubility of the ammonium sulfate side product can be
controlled to less than 6% in the hydroxylamine product solution
after filtration.
TABLE-US-00002 TABLE 2 Results of analysis on products from Example
4 33% HAS HAS NH.sub.3 added Filtrate HA NH.sub.3 HAS AmS Test #
(g) crystal (g) (g) (g) (wt %) (wt %) (wt %) (wt %) 1 241.39 0
122.61 261.53 11.729 19.021 1.54 8.22 2 240.72 156.95 176.67 287.21
30.79 23.95 0.12 5.14 3 490.0 304.0 310.0 594.0 30.66 16.68 0.08
5.80 4 490.0 302.0 396.0 640.0 26.35 22.62 0 2.07
TABLE-US-00003 TABLE 3 Results of analysis on products from Example
4 (continued) Filter cake Dried filter AmS Yield based Yield based
Yield based Test# (g) cake (g) HAS (g) (g) on HA (%) on AmS (%) on
HAS (%) 1 70.46 55.30 0 55.07 95.69 119.38 94.94 2 246.97 199.84
2.49 173.32 92.95 98.84 98.81 3 426.0 333.57 10.36 334.26 97.17
94.86 97.67 4 442.0 353.00 9.70 355.30 90.95 98.73 97.91
EXAMPLE 5 (INVENTION)
397 grams of a base solution containing 18.6% of ammonia were
introduced into a 1-liter jacketed reactor. After the reactor was
cooled to 5.0.degree. C., 461 grams total of hydroxylammonium
sulfate were added to the reactor in five (5) steps. Both the
reactor temperature and the pH of the neutralization solution were
monitored as illustrated in FIGS. 1 and 2. As the pH decreased from
about 13.3 to 9, ammonia was introduced to the reactor at a flow
rate of 5 liters per minute until the pH of the product solution
reached 12.5. The reaction product was separated into two portions
by a vacuum filtration: a filtrate and a filter cake. The filtrate
was analyzed for hydroxylamine, ammonia, hydroxylammonium sulfate
and ammonium sulfate by a titration method.
The filter cake was dried in an oven at 105.degree. C. for a period
of more than 15 hours. The dried filter cake was dissolved in water
and the contents of ammonium sulfate (AmS) and hydroxylammonium
sulfate (HAS) were determined by titration. Reaction yields were
calculated using analytical results obtained for HA, AmS and HAS as
shown in Tables 4 and 5 for 4 repeat runs. Results of this example
show that unexpectly a yield of 90% and higher can be achieved by
neutralizing hydroxylamine sulfate with a weak base such as ammonia
and the solubility of the ammonium sulfate side product can be
controlled to less than 6% in the hydroxylamine product solution
after filtration.
TABLE-US-00004 TABLE 4 Results of analysis on products from Example
5 Ammonia Ammonia water conc. HAS NH.sub.3 Filtrate HA NH.sub.3 HAS
AmS Test # (g) (wt %) crystal (g) added (g) (g) (wt %) (wt %) (wt
%) (wt %) 1 397 18.6 461 268 544 26.51 16.29 0.163 5.60 2 399 18.6
465 293 555 27.13 20.13 0 2.54 3 400 21.0 481 250 459 30.42 17.62 0
5.68 4 429 18.6 482 205 545 27.56 18.70 0 6.03
TABLE-US-00005 TABLE 5 Results of analysis on products from Example
5 (continued) Filter cake Dried filter AmS Yield based Yield based
Yield based Test # (g) cake (g) HAS (g) (g) on HA (%) on AmS (%) on
HAS (%) 1 506 340 24.34 335.85 82.42 98.71 94.53 2 498 399 17.99
326.38 91.29 90.96 96.13 3 558 348 45.09 304.53 84.62 85.37 90.63 4
499 359 31.16 315.68 86.25 91.72 93.40
EXAMPLE 6 (INVENTION)
Following a general procedure of Example 5, about 400 grams of an
ammonium hydroxide solution containing 29.3% of ammonia were
neutralizaed with about 750 grams of crystalline hydroxylammonium
sulfate. The hydroxylammonium sulfate were added to the reactor in
eight (8) steps (equal parts). Both the reactor temperature and the
pH of the neutralization solution were monitored as illustrated in
FIGS. 3 and 4. As the pH decreased from about 13.3 to 9, ammonia
gas was introduced to the reactor at a flow rate of 5 liters per
minute until the pH of the product solution reached 12.2. The
reaction product was separated into two portions by a vacuum
filtration: a filtrate and a filter cake. The filtrate was analyzed
for hydroxylamine, ammonia, hydroxylammonium sulfate and ammonium
sulfate by a titration method.
The filter cake was dried in an oven at 105.degree. C. for a period
of more than 15 hours. The dried filter cake was dissolved in water
and the contents of ammonium sulfate (AmS) and hydroxylammonium
sulfate (HAS) were determined by titration. Reaction yields were
calculated using analytical results obtained for HA, AmS and HAS as
shown in Tables 6 and 7 for 5 runs. Results of this example show
that again a yield of 90% and higher can be achieved by
neutralizing hydroxylamine sulfate with a weak base such as ammonia
and the solubility of the ammonium sulfate side product can be
controlled to less than 5% in the hydroxylamine product solution
after filtration. In addition, an HA solution of greater than
(>) 50% by weight can be prepared in one neutralization step
after the removal of the excess ammonia and the dissolved ammonium
sulfate.
TABLE-US-00006 TABLE 6 Results of analysis on products from Example
6 Ammonia Ammonia water conc. HAS NH.sub.3 Filtrate HA NH.sub.3 HAS
AmS Test # (g) (wt %) crystal (g) added (g) (g) (wt %) (wt %) (wt
%) (wt %) 1 406 29.3 750 308 557 38.80 19.99 0 4.94 2 405 29.3 761
327 491 37.50 20.60 0 3.88 3 413 29.3 760 292 553 38.36 19.61 0
4.38 4 421 29.3 762 304 525 37.51 17.86 0.61 2.20
TABLE-US-00007 TABLE 7 Results of analysis on products from Example
6 (continued) Filter cake Dried filter AmS Yield based Yield based
Yield based Test # (g) cake (g) HAS (g) (g) on HA (%) on AmS (%) on
HAS (%) 1 820 578 52.59 524.01 87.08 91.35 92.99 2 885 640 88.32
477.18 73.38 81.00 88.39 3 828 614 71.06 502.23 83.47 86.04 90.65 4
865 632 52.59 524.01 79.28 87.30 92.68
EXAMPLE 7 (INVENTION)
300 mL of product mixture solutions prepared in Example 3 were
treated with 160 mL of ion-exchange resins. 80 mL each from Rohm
and Haas Amberjet 4400 and Mitsubishi SAT 20L sequentially. This
was repeated again and then treated with 80 mL of Rohm and Haas
Amberjet 1500 and 160 mL of Mitsubishi SKT 20L. The resulting
solution from the ion-exchange process was analyzed along with the
solution after filtration for metal impurities with an ICP-MS
[inductive coupled plasma--mass spectrometry] instrument. Results
of the metal analysis are shown in Table 8 along with those of an
"18 Megohm" water.
TABLE-US-00008 TABLE 8 Results of ICP-MS analysis on the product
from Example 5 18 Megohm Filtered Metals water HA product
Ion-exchanged sample Na (ppb) 0.077 136.4 3.54 Co (ppb) 0.045 2.22
0.094 Ni (ppb) 0.43 29.73 0.52 Cu (ppb) 0.11 1.43 0.72 Fe (ppb)
0.23 619.2 4.99
EXAMPLE 8 (INVENTION)
Following a general procedure of Example 7, the ion-exchange
process was followed with the product pH measurement and titration
analysis. 300 mL of HA product from Example 3 were treated with
Rohm and Haas ion-exchange resins: Amberjet 4400 and Amberjet 1500
["R&H"] sequentially . Analytical results on the ion-exchanged
products are summarized in Table 9.
TABLE-US-00009 TABLE 9 Results of titration analysis on products
from Example 5 Sample Total R&H Total R&H HAS
(NH.sub.4).sub.2SO.sub.4 number 4400 (mL) 1500 (mL) pH (wt %) (wt
%) NH.sub.3 (wt %) HA (wt %) 1 80 80 8.95 0 9.71 2.88 10.72 2 240
80 9.09 0 4.35 2.16 9.65 3 240 160 9.11 0 4.21 1.22 8.39 4 320 160
9.06 0 1.94 1.53 7.58
EXAMPLE 9 (INVENTION)
300 mL of the ion-exchanged hydroxylamine solution from Run number
1 of Example 4 were distilled under vacuum (200 torrs to 8 torrs,
or 26.6 kPa to 1.1 kPa) at 35.degree. C. for 80 minutes in a rotary
evaporator. The resulting distillation bottom was analyzed with an
automatic titrator. Results are shown in Table 8 along with that of
the starting solution.
TABLE-US-00010 TABLE 10 Results of titration analysis on products
from Example 8 HAS (NH.sub.4).sub.2SO.sub.4 NH.sub.3 HA Sample pH
(wt %) (wt %) (wt %) (wt %) Starting feed 8.97 0 8.83 3.60 10.36
Mother liquor 6.64 28.93 15.54 0 36.01
These results show that during the vacuum distillation NH3 was
completely removed. With a pH of 6, the reversion of ammonium
sulfate to hydroxylamine sulfate occurred.
All the examples are intended for illustration purpose only. Those
skilled in the art will readily recognize and appreciate that many
modifications and variations can be made and such modifications and
variations are encompassed within the scope and spirit of the
present invention as defined by the written disclosure and the
accompanying claims.
* * * * *